In general, the designation "high-temperature storage battery" refers to a battery which is capable of operating in high temperature environments, for instance, at temperatures above the melting point of the electrolyte contained therein. It has been found that various high-temperature batteries can be manufactured using varied combinations of various materials for electrode, separators, and/or electrolytes. Among the high-temperature storage batteries hitherto proposed, those expected to be most active, with respect to performance and utility, are those which employ an alkali or alkali earth metal or an alloy of one of those metals with another more stable metal as an active material for the negative electrode, a metal sulfide and oxide as an active material for the positive electrode, and molten salts containing at least one of the above alkali or alkali earth metal ions. In those batteries, for example, lithium, sodium or calcium, or an alloy of one of those metals with aluminum or silicone is used as an active material for the negative electrode, and iron sulfide, copper sulfide, nickel sulfide, cobalt sulfide or a combination of those sulfides is employed as an active material for the positive electrode. However, it is important to understand that the performance characteristics of a battery, such as its life cycle, energy and power, greatly demands upon the structure of the battery. Thus, various batteries having different structures have been developed to data.
Many prior art attempts have been made to improve battery structure. For example, in U.S. Pat. No. 3,887,396 issued on Nov. 15, 1973, there is proposed a battery of a button type configuration, the height of which is much lower than the diameter. The electrodes installed in the battery have the shape of disc plates and are horizontally assembled by interposing a separator between the positive and negative electrodes. However, in this battery, an electrode terminal must extend outward from one of the electrodes and, therefore such a battery requires a complex electrode structure.
U.S. Pat. No. 3,933,520 granted to E. C. Gay and F. J. Martino on Apr. 3, 1975, discloses a method of preparing electrodes for use in a high-temperature battery. The method comprises first preparing a structure of reticulated or porous current collectors in the shape of an electrode and then distributing electrode active materials into said structures. However, batteries using the electrodes thus prepared, due to protruded points of the current collector, are apt to be damaged during operation.
Another U.S. Pat. No. 3,933,521 to D. R. Vissers and B. J. Tani, issued Jan. 20, 1976, has proposed an electrode structure wherein metallic fiber is compacted into a current collector made of metallic screen and a molten alkali metal is placed into the interstitial crevices of the metallic fiber. In the electrode design, both sides of the collector are used to increase the surface area of the current collector. However, in general, molten alkali metals are highly corrosive and, therefore, many problems are encountered in the selection of anti-corrosive materials, particularly in their mechanical stability in response to impact.
Similarly, J. C. Hall has proposed, in his U.S. Pat. No. 4,003,735 issued Jan. 18, 1977, an electrode, which was provided by compacing an active material into a tetragonal, pentagonal, circular, or honeycomb-like current collector structure so that the material can be retained in the collector. A battery using such an electrode also has some commercialization problems due to its complicated structure and difficulties in evenly compacting the active materials onto the surface of the electrode. In addition, U.S. Pat. No. 4,029,860 to D. R. Vissers, et al., discloses an electrode structure constructed by attaching reticulated or parallel band-shaped small structures to the whole area of current collectors; electrode active materials are compacted therebetween. A battery employing this electrode also has similar drawbacks as in Hall's electrode mentioned above. A battery using a refractory material, i.e. woven oxides or nitrides, as a separator which is inserted between electrodes (See: Progress Report for the Period, Argonne National Laboratory--78-74, Oct. 1977--Sep. 1978, and Development of Lithium-metal Sulfide Batteries, EPRI EM-176, Interim Report, June, 1978) or using magnesium oxide power as a separator substitute (See: Extended Abstracts Electrochem. Soc. Meeting, Pittsburgh PA, Oct. 15-20, 78(2), 418, 1978) is under active development. For instance, for a lithium-iron sulfide battery, cloths made of a boron nitride or ytrium oxide, or non-woven fabrics are used; however, since it is difficult to obtain a woven fabric from the above nitride or oxide, and since the material itself is expensive, the use of the material is not desirable in view of economy of manufacture. As a substitute for the highly expensive material, pulverized magnesium oxide having desirable properties of hear-resistance and chemical resistance has therefore been increasingly used; however, since the separator layer of the powder is apt to be broken in the structure of a quadrilateral or cylindrical battery, it is not easy to apply the powder separator technique for actual battery production.
Additional difficulties encountered in conventional battery design are due to the fact that since a plurality of current collectors of the flat plate, honeycomb or network types must be arranged in parallel for each group of positive and negative electrodes connected in the cell and each terminal post from the group of connected positive and negative electrodes should be extended out of the cell, the connected points tend to break off.
From the foregoing, it can be concluded that conventional batteries can be manufactured to provide high-performance characteristics with high-energy and high-power density. With respect to reliability and cost, however, it will be understood that there are still many problems to be solved in order to obtain practical batteries.
Furthermore, in a battery employing a certain conventional electrode structure, increased amounts of materials are required which do not take part in the electrode reaction, thereby causing increased battery weight and reduced energy density of the battery.